Such orthoses, previously known as “elasticated” stockings or socks or “elasticated” tights, are textile medical devices that produce a therapeutic effect by compression of the lower limbs, in contrast to “posture” stockings (or indeed “support” stockings or “anti-tiredness” stockings), and to “fashion” stockings, which are not medical devices with a therapeutic purpose.
EVC orthoses are designed to produce a therapeutic effect by compressing the lower limb over a greater or lesser extent, usually with a profile that is degressive going upwards from the ankle. Depending on the type of orthosis, the pressure measured at the ankle may lie in the range 10 millimeters of mercury (mmHg) to more than 36 mmHg (i.e. 13 hectopascals (hPa) to 48 hPa, where the unit mmHg is nevertheless in widespread use for measuring pressure in the field of phlebology and medical compression). In France, stockings are subdivided into four textile classes in the ASQUAL system, namely class I (13 hPa to 20 hPa≈10 mmHg to 15 mmHg at the ankle), class II (20 hPa to 27 hPa≈15 mmHg to 20 mmHg), class III (27 hPa to 48 hPa≈20 mmHg to 36 mmHg), and class IV (>48 hPa≈>36 mmHg). These compression classes may be different in other countries.
In order to enable the lower limbs to be subjected to strong compression, such orthoses are made from a knit that presents a texture that is tight to a greater or lesser extent with an incorporated elastic weft yarn, generally a covered spandex.
More precisely, under the effect of being on the limb, the stretch textile of the orthosis exerts compression that results from the return force of the elastic fibers making up the material, and the application of those elastic return forces against the perimeter of the outline generates a local pressure at a given point that is inversely proportional to the radius of curvature at the outline at said point, in application of the Laplace-Young equation.
This pressure is the “textile pressure” as defined and calculated in the meaning of French standard NF G 30-102, part B. The term “pressure” is used in the present description to designate the mean, at a given altitude, of the standardized pressures exerted locally along an outline of the leg (which outline may be circular or elliptical in the approximation of a leg model).
The knit and the yarns, and also the size of the rows of stitches are selected so as to apply predetermined pressures at different altitudes up the lower limb, e.g. at the height of the ankle, at the start of the calf, over the calf, at the popliteal space, etc., all the way up to the top of the thigh, which altitudes are conventionally written B, C, . . . , G. These various pressures are defined for each class with reference to metrological jigs such as the leg model of French standard NF G 30-102 part B, Appendix B, corresponding to the leg model of the “Hohenstein” type in the German reference RAL-GZ 387.
The above-mentioned characteristic of the pressure profile being degressive consists in exerting a maximum pressure at the ankle and then a pressure that is degressive going from the ankle to the calf or to the thigh. It relies on the fact that in the orthostatic situation the intravenous pressure is degressive from the ankle to the calf and to then to the thigh. In the event of chronic venous insufficiency, the elastic compression exerted by the orthosis on the limb induces an anti-stasis effect encouraging venous return.
More precisely, physiologically speaking, the calf is the key element of venous hemodynamics of the lower limbs and of chronic venous pathology.
The importance of the effect of the “muscle pump” or the “calf musculo-aponeurotic pump” (CMAP) have been described in terms of return venous blood flow, where physiological cycles of the calf muscles contracting and relaxing give rise, via opening and closing of valves of the veins, to emptying and filling of the venous network of the lower limb. The efficiency of CMAP decreases progressively with a subject's age, thereby naturally aggregating chronic venous insufficiency.
Chronic venous insufficiency is characterized by a failure of this muscle pump effect. When the insufficiency is severe, the ankle is also involved, because of deep refluxes or by Cockett's perforators, which play a major role in trophic disorders and ulcers.
The starting point of the invention is the search for means enabling the efficiency of the CMAP to be improved or for it to be taken over by a compressive orthosis that is better adapted to this role than are the orthoses that have been proposed in the past.
The prejudice whereby a stocking should exert maximum pressure at the ankle and then pressure that is degressive going from the ankle to the calf or to the thigh is based on the way intravenous pressures are distributed in the orthostatic situation. In that situation, the effect of gravity causes intravenous pressure to be degressive from the ankle to the thigh, whence the need for matching compression.
However, studies on venous physiology, in particular using recent tools for modeling and simulating containment such as those described in WO 2006/087442 A1 (Laboratoires Innothera), show that the effectiveness of an EVC orthosis, providing it is possible to make the CMAP operate, lies rather in improving its efficiency.
FR 2 824 471 B1 (Rodier) describes an approach consisting in providing “elective compression/containment” by means of a multizone stocking with different knits, associating a region with a very elastic knit over the foot and the ankle followed by a region with a knit that presents little elasticity from the bottom of the calf up to the popliteal space, and extended by a region in which the knit is once more very elastic from the knee to the top of the thigh. The basic idea consists in providing zones with a compressive effect (foot, ankle, and thigh) on either side of a zone with an effect that is more one of containment (calf). This zone of the orthosis produces less effect at rest than those on either side of it, however during contractions of the calf muscle it exerts increased compression, thereby increasing the power and reinforcing the emptying effect of the CMAP.
In this respect, it should be specified that the terms “compression” and “containment” define two effects that are clearly different, even though they are sometimes confused in everyday speech:                “compression” is the effect produced by an elastic orthosis both at rest and when making an effort, on a limb segment as a result of more or less strong return forces from the elastic fibers of the orthosis. These forces act in almost constant manner on the limb: at rest, the compression is present at the nominal pressure value and when making an effort the effect of the compression is increased by the contraction of the muscle masses; and        conversely, “containment” is the effect produced by an orthosis that acts in different manners between making an effort and being at rest on a limb segment under the action of a structure that is considered as being inelastic, e.g. a non-elastic bandage, also referred to as a “short-stretch bandage”. At rest, that type of bandage exerts low or zero pressure; in contrast, during muscular contraction, it opposes local increases in the volume of the calf that comes into abutment against the non-elastic structure, so pressure is thus increased. Containment is thus effective and it is active while making an effort and practically inactive while at rest.        
It is in order to distinguish between these two notions that the respective terms “compression” (or “compressive”) and “containment” (or “containing”) are used.
Concerning these definitions, the proposal of above-mentioned FR 2 824 471 B1 that makes use only of yarns and stitches that are elastic to a greater or lesser extent over the height of the orthosis produces a containment effect level with the calf, but to a very partial extent only.
It comprises rather zones that are all elastic but that present different degrees of elasticity, as has also been proposed in EP 0 934 043 B1 (Couzan) or EP 1 240 880 A2 (Stolk). Those last two documents teach making a stocking or a sock with a zone that is less rigid (more elastic) in the region of the calf, respectively in uniform manner over the entire circumference of the calf, or only in the posterior region thereof.
In addition, from a technological point of view, all of those prior art “multizone” structures are found to be difficult to make in practice, given the difficulty that exists in setting the knitting machine so as to obtain the required variable elasticity profiles, with transitions that are very abrupt between very non-uniform textures that correspond to the different zones of the stocking or the sock.
Furthermore, and above all, those orthoses that may be referred to as “semi-containment” are not specifically adapted to a given patient. Concretely, the practitioner is content merely to select an orthosis from a grid of sizes after measuring the perimeter of the ankle and of the calf. In practice, this leads to a compromise solution that does not take the real morphology of the calf into account, which morphology may vary widely from one patient to another and cannot be described suitably merely by measuring the maximum perimeter of the calf.
This drawback is particularly troublesome with products that are supposed to produce a containment effect, since the reinforcement of the effect of the CMAP depends on the non-elastic structure being a good fit to the limb segment in question, over the entire extent thereof: if the non-elastic structure is not in close contact with the limb at rest, then it will procure very little effect for a small or moderate increase in the volume of the muscle; on the contrary, if it is too small, then it will exert stress on the limb even at rest, with harmful effects on blood circulation, in addition to providing the wearer with a binding effect that runs the risk of making the orthosis particularly uncomfortable for the patient.
It thus appears to be desirable to be able to make orthoses that provide a genuine containment effect on the calf via a structure that is not elastic (as opposed to a structure of reduced elasticity) and that fits the exact morphology of the limb segment of each patient.
If it is desired to have a containment product that is rigid and made-to-measure, specifically fitting the patient, a first solution consists in using multilayer bandages, with the well-known difficulty of adjusting the bandage properly, since it must not be too tight (which would squeeze the calf) nor too loose (which would not produce any effect), thereby producing a result that is highly “operator-dependent”. As explained above, the fitting of a rigid containment product is highly critical, unlike a compressive elastic structure which is much more tolerant.
In addition, the bandage needs to be readjusted regularly, and on each occasion with the same care in order to secure a good fit.
For these reasons, patients generally prefer to use some other solution, in the form of a knitted orthosis for putting on in more convenient manner and of better appearance.
The problem is then that of fabricating a product that is rigid and made-to-measure, being an exact fit to the particular morphology of the patient. The technique consists in taking the most complete possible measurements of the calf, with circumferences at several altitudes. The orthosis is then knitted on a flat knitting machine and is shaped by sewing a seam all along its length, thereby requiring an additional manufacturing step. It can be understood that such a complete made-to-measure technique is lengthy to implement, complicated, and therefore expensive, and it does not enable rigid containment products to become widespread, in spite of their manifest therapeutid advantages.